Field of the Disclosure
Embodiments of the present application relates to the art of a control system and a control method for an automatic vehicle transmission configured to change a speed ratio stepwise.
Discussion of the Related Art
U.S. Pat. No. 5,697,864 describes a shift control apparatus for an automatic vehicle transmission configured to carry out a skip shift of two stages or more. The transmission taught by U.S. Pat. No. 5,697,864 includes a first transmission gear unit equipped with a clutch to clutch shift mechanism, and a second transmission gear unit equipped with a clutch to one-way clutch shift mechanism. According to the teachings of U.S. Pat. No. 5,697,864, the shift control apparatus controls the clutch-to-clutch shift mechanism and the clutch to one-way clutch shift mechanism in such a manner that rotational synchronization of the clutch to one-way clutch shift mechanism is caused to take place earlier than or at the same time as rotational synchronization of the clutch to clutch shift mechanism when gear shifting is effected over the first and second transmission gear units.
US 2014/0088789 describes an evaluation method for a shift feeling of a vehicle in which a shift feeling felt by an occupant when a vehicle is accelerated-shifted is quantified objectively by using human sensibility ergonomic concept. According to the teachings of US 2014/0088789, an initial acceleration response time, a final acceleration arriving time, an average acceleration maintaining amount during a predetermined time period after arriving a maximum acceleration, an acceleration rising slope, an initial maximum jerk and an end maximum jerk are detected as measurement factors. Then, four sensory factors of a responsiveness, a strength, a smoothness and an unperceivable are calculated by multiplying the six measurement factors by different arithmetic coefficients, respectively, and summating them.
JP-A-2013-87800 describes a dual clutch type automatic transmission and a gear shift control method thereof. According to the teachings of JP-A-2013-87800, an interim gear stage of a skip downshift is determined based on a predictive vehicle acceleration.
During execution of downshifting, acceleration is increased after an inevitable delay depending on a gear stage or a speed change pattern. For this reason, if an order of executing shifting operation of the first and the second transmissions is fixed as taught by U.S. Pat. No. 5,697,864 to achieve a skip downshift across at least one stage, it may take a longer time to increase the acceleration to an extent that a driver can sense the acceleration. According to the teachings of US 2014/0088789, a speed change rate is considered as the response time to evaluate a shift feeling. In this case, an elongation of a speed change period may downgrade the evaluation of the shift feeling.
The above-explained disadvantages may be solved by setting an interim gear stage during the skip downshift as taught by JP-A-2013-87800. In this case, the interim gear stage may be determined in such a manner as to improve a shifting response to carry out the skip downshift without delay. However, the skip downshift may be executed stepwise from an initial gear stage to the interim gear stage, and from the interim gear stage to the target gear stage. In this case, therefore, the drive may feel a shock during the skip downshift.